Segmented illumination and polarization devices for tunable optical metasurfaces

ABSTRACT

According to various embodiments, a solid-state light detection and ranging (LiDAR) transmitter includes a tunable optical metasurface to selectively steer incident optical radiation long an azimuth axis. In some embodiments, different subsets of lasers in an array of lasers are activated to generate optical radiation for incidence on the metasurface at different angles of incidence on an elevation axis for unsteered deflection by the metasurface at corresponding angles of elevation. In some embodiments, a prism is positioned relative to the tunable optical metasurface to deflect the optical radiation from the optical assembly by the optical radiation source for incidence on the metasurface at an angle of incidence that is between the first steering angle and the second steering angle, such that the optical radiation incident on the metasurface and the steered output optical radiation from the metasurface spatially overlap within the prism.

TECHNICAL FIELD

This disclosure relates to optical metasurfaces, including liquidcrystal metasurfaces used for solid-state light detection and ranging(LiDAR).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a tunable liquid crystal metasurface(LCM), according to one embodiment.

FIG. 2A illustrates a side view of an optical path of a transmitter of asolid-state LiDAR system, according to one embodiment.

FIG. 2B illustrates a top view of an example optical path of thesolid-state LiDAR system.

FIG. 3 illustrates a block diagram of a transmit metasurface with anangle of incidence, according to one embodiment.

FIG. 4A illustrates an array of vertical-cavity surface-emitting lasers(VCSELs), according to one embodiment.

FIG. 4B illustrates an array of offset rows of VCSELs, according to oneembodiment.

FIG. 5 illustrates an example of edge emitter light sources, accordingto one embodiment.

FIG. 6A illustrates an example of rows of VCSEL sources, according toone embodiment.

FIG. 6B illustrates another example of offset rows of VCSEL sources,according to one embodiment.

FIG. 6C illustrates a tunable optical metasurface to steer incidentoptical radiation from an array of VCSEL sources, according to oneembodiment.

FIG. 6D illustrates examples of far-field illumination via full andpartial activation of rows of VCSEL sources, according to oneembodiment.

FIG. 7A illustrates an example of partial elevation illumination ofsteered optical radiation by partial activation of a VCSEL array,according to one embodiment.

FIG. 7B illustrates another example of partial elevation illumination ofsteered optical radiation by activation of a different subset of theVCSEL array, according to one embodiment.

FIG. 7C illustrates another example of partial elevation illumination ofsteered optical radiation by activation of a different subset of theVCSEL array, according to one embodiment.

FIG. 7D illustrates an example of complete elevation illumination ofsteered optical radiation by activation of a different subset of theVCSEL array, according to one embodiment.

FIG. 8 illustrates an example of an optical assembly for polarizationspatial combining of optical radiation from an unpolarized source,according to one embodiment.

FIG. 9 illustrates another example of an optical assembly forpolarization spatial combining of optical radiation from an unpolarizedsource, according to one embodiment.

FIG. 10 illustrates another example of an optical assembly forpolarization spatial combining of optical radiation from an unpolarizedsource, according to one embodiment.

FIG. 11 illustrates another example of an optical assembly forpolarization spatial combining of optical radiation from an unpolarizedsource, according to one embodiment.

FIG. 12A illustrates two beams overlaid in the same plane using a halfwaveplate for the S-pol beam path through a prism to a metasurface,according to one embodiment.

FIG. 12B illustrates another view of optical radiation directed throughthe prism to the metasurface, according to one embodiment.

FIG. 12C illustrates a side view of the optical radiation directedthrough the prism to the metasurface, according to one embodiment.

FIG. 12D illustrates the side view of the optical radiation transmissionsystem steered to a steering angle, according to one embodiment.

FIG. 12E illustrates the side view of the optical radiation transmissionsystem steered to a third steering angle at which the transmittedoptical radiation overlaps the optical radiation incident on themetasurface, according to one embodiment.

FIG. 13A illustrates example components of an optical prism assembly,according to various embodiments.

FIG. 13B illustrates an optical path through the optical prism assembly,according to one embodiment.

FIGS. 14A-D illustrate example views of a transmissive (e.g.,refractive) metasurface with a half waveplate, according to variousembodiments.

FIGS. 15A-D illustrate example views of a reflective metasurface with ahalf waveplate, according to various embodiments.

FIGS. 16A-B illustrate examples of metasurface transmitters utilizinglow-angle optical assemblies to convey optical radiation to ametasurface, according to various embodiments.

FIG. 16C illustrates an example of a metasurface transmitter with adiffuser to diffuse unsteered optical radiation, according to oneembodiment.

FIGS. 17A-24 illustrate examples of optical transmitters utilizingprisms to convey optical radiation to a tunable metasurface from opticalradiation sources in various locations relative to the metasurface,according to various embodiments.

FIGS. 25A-C illustrates a comparison of low-angle “prismless” opticalassemblies with prism-based optical assemblies at various steeringangles, according to various embodiments.

FIG. 26 illustrates an example of an optical transmitter with a prismand a tunable metasurface, according to one embodiment.

FIG. 27A illustrates an example of an optical transmitter with a prism,a tunable metasurface, and a cylindrical defocusing lens, according toone embodiment.

FIG. 27B illustrates an example embodiment of a LiDAR system using theoptical transmitter of FIG. 27A, according to one embodiment.

FIGS. 28A-C illustrate examples of optical field-of-view (FOV) expandingassemblies for use with the optical transmitter systems describedherein, according to various embodiments.

FIG. 29 illustrates the range of straight and curved transmit scan linesof a low-angle, “prism less” metasurface at various steering angles,according to one embodiment.

FIG. 30 illustrates the range of straight and curved transmit scan linesof a metasurface with a prism, according to one embodiment.

FIG. 31 illustrates the curvature of transmit scan lines in thefar-field using an optical transmitter with a tunable metasurface, aprism, and an optical FOV expander, according to one embodiment.

FIG. 32 illustrates an example of a receive lens with barrel distortionto compensate for inherent pincushion distortion of transmit scan linessuch that detected optical radiation is aligned in straight lines on asensor, according to one embodiment.

DETAILED DESCRIPTION

Tunable optical metasurfaces may be used for beamforming, includingthree-dimensional beam shaping, two-dimensional beam steering, andone-dimensional beam steering. The presently described systems andmethods can be applied to tunable metasurfaces utilizing variousarchitectures and designs. In general, a metasurface includes aplurality of optical structures that, together with a tunable dielectricmaterial, can be operated to deflect (e.g., reflect, refract, steer,defocus, focus, converge, diverge, etc.) optical radiation within anoperational bandwidth.

Various specific examples of tunable optical metasurfaces are describedherein and depicted in the figures. For example, in one specificembodiment, a tunable optical metasurface includes an array of elongatedrails (e.g., resonators) arranged parallel to one another with respectto an optical reflector, such as an optically reflective metal layer ora Bragg reflector. In such an embodiment, the elongated rails may beformed from metal, a doped semiconductor material, and/or a dielectricmaterial and be configured with subwavelength interelement spacings.

Examples of suitable metals that may be used as optical reflectors andoptical structures in a metasurface include, but are not limited to,copper, aluminum, gold, silver, platinum, titanium, and chromium. Inembodiments in which the elongated rails are copper, the elongatedcopper rails may, for example, be formed using a copper damascenemanufacturing process, followed by etching the intermetal dielectric andsubsequent passivation of the copper. Examples of suitable fabricationprocesses that can be adapted for use with the presently describedsystems and methods are described in, for example, U.S. Pat. No.10,968,522 granted on Apr. 6, 2021, which is hereby incorporated byreference in its entirety.

Liquid crystal, or another refractive index tunable dielectric material,is positioned in the gaps or channels between adjacent rails (e.g.,doped semiconductor or metal rails). Liquid crystal is used in many ofthe examples provided in this disclosure. However, it is appreciatedthat alternative dielectric materials with tunable refractive indicesand/or combinations of different dielectric materials with tunablerefractive indices may be utilized instead of liquid crystal in manyinstances.

For the sake of clarity and to avoid unnecessary repetition, thealternative dielectric materials are not called out in connection withevery example provided herein. Nevertheless, the use or substitution ofalternative tunable dielectric materials in each of the examplesprovided herein is explicitly contemplated and encompassed by thisdisclosure. Examples of dielectric materials with tunable refractiveindices suitable for use in the various example metasurfaces describedherein include but are not limited to various forms and combinations ofliquid crystal, electro-optic polymers, chalcogenide glasses, otherphase change materials, and semiconductor materials.

In some embodiments, an optically tunable metasurface includes atwo-dimensional array of pillars instead of (or possibly in combinationwith) elongated rails. Regardless of the exact optical structuresutilized in the metasurface, the tunable metasurface may include liquidcrystal or another refractive index tunable dielectric material in,around, between, and/or on the optical structures. For example, liquidcrystal may fill the channels between resonator rails, fill the gapsbetween neighboring pillars, and/or form a layer of liquid crystal abovethe rails or pillars. Examples of suitable metals that may be used asoptical reflectors and optical structures in a metasurface include, butare not limited to, copper, aluminum, gold, silver, platinum, titanium,and chromium.

In various embodiments, biasing the liquid crystal in a metasurface witha pattern of voltage biases changes the reflection phase and amplitudeof the optical radiation (or transmission phase). For example, inembodiments using reflective-type metasurfaces, biasing the liquidcrystal in the metasurface with a pattern of voltage biases can be usedto change the reflection phase and amplitude pattern of opticalradiation reflected by an underlying reflector layer. Each differentvoltage pattern applied across the metasurface corresponds to adifferent reflection phase pattern (or transmission phase pattern intransmissive designs). With a one-dimensional array of opticalstructures (such as a one-dimensional array of resonator rails), eachdifferent reflection phase pattern corresponds to a different steeringangle or radiation pattern in a single dimension. A digital or analogcontroller (controlling current and/or voltage), such as a metasurfacedriver, may apply a voltage differential bias pattern, such as a blazedgrating pattern, to the metasurface to achieve a target beam shaping,such as a target beam steering angle. The term “beam shaping” is usedherein in a broad sense to encompass one-dimensional beam steering,two-dimensional beam steering, wavelength filtering, beam divergence,beam convergence, beam focusing, and/or controlled deflection,refraction, reflection, and/or arbitrary phase and amplitude control ofincident optical radiation.

According to various embodiments, the driver circuit of the tunableoptical device comprises a one-dimensional passive matrix controllerwith driver channels integrated within the substrate to individuallycontrol each optical structure of the metasurface. In other embodiments,the optical structures of the metasurface are arranged as tiled subsetsof optical structures, where each tile shares a set of common controlinputs. As described in some of the applications incorporated herein byreference, each tile of optical structures may include tens, hundreds,thousands, or millions of optical structures. Each tile may becontrolled by a common set of control lines, such that the number ofunique control inputs for the metasurface is much fewer than the totalnumber of optical structures in the metasurface. The driver circuit mayinclude control lines or driver channels integrated within the substrateto control each individual tile of optical structures.

It is appreciated that the metasurface technologies described herein mayincorporate or otherwise leverage prior advancements in surfacescattering antennas, such as those described in U.S. Patent PublicationNo. 2012/0194399; U.S. Patent Publication No. 2019/0285798, U.S. PatentPublication 2018/0239213, and U.S. Patent Publication No. 2018/0241131,which publications are hereby incorporated by reference in theirentireties. Additional elements, applications, and features of surfacescattering antennas that feature a reference wave or feed wave aredescribed in U.S. Patent Publication Nos. 2014/0266946, 2015/0318618,2015/0318620, 2015/0380828, 2015/0162658, and 2015/0372389, each ofwhich is hereby incorporated by reference in its entirety. Specificdescriptions of optical resonant antenna configurations and featuresizes are described in U.S. patent application Ser. Nos. 15/900,676,15/900,683, 15/924,744, and 17/685,621, each of which is herebyincorporated by reference in its entirety.

Throughout this disclosure, examples of transmitting (or receiving)embodiments are provided with the understanding that reciprocalreceiving (or transmitting) embodiments are also contemplated. Forexample, metasurface and optical assembly configurations described astransmitting optical radiation from an optical radiation source can beused in reverse to receive optical radiation for detection by a sensor.Similarly, it is understood that a system may operate as only atransmitter, only a receiver, simultaneously as a transmitter andreceiver, with a time-multiplexed transmitter/receiver, with afrequency-multiplexed transmitter/receiver, with the first metasurfaceacting as a transmitter and a second metasurface acting as a receiver,or another transmit/receive configuration or operation technique.Similarly, many of the examples are described in terms of modifying areflection phase pattern of a reflective-type metasurface. However, itis appreciated that many of the approaches, techniques, systems,methods, and principles taught herein can be applied totransmissive-type metasurfaces as well. Accordingly, each embodiment inwhich a reflective-type metasurface is described should be understood asimplicitly teaching a corresponding embodiment using a transmissive-typemetasurface, except when the specific optical assembly described isdependent upon the specifically described transmissive-type orreflective-type metasurface.

The presently described embodiments support optical bandwidths and are,for example, suitable for optical sensing systems such as LiDAR, opticalcommunications systems, optical computing systems, optical powertransfer, and displays. For example, the systems and methods describedherein can be configured with metasurfaces that operate in thesub-infrared, mid-infrared, high-infrared, and/or visible-frequencyranges (generally referred to herein as “optical”). Given the featuresizes needed for sub-wavelength optical antennas and antenna spacings(e.g., sub-wavelength interelement spacings), the described metasurfacesmay be manufactured using micro-lithographic and/or nano-lithographicprocesses, such as fabrication methods commonly used to manufacture CMOSintegrated circuits.

Additionally, many of the described embodiments of metasurfaces aredescribed in terms of controlling, tuning, or modifying phase patterns(e.g., reflection phase patterns or transmission phase patterns).However, many of the embodiments may be used in conjunction withmetasurfaces in which the optical elements are tuned or adjusted tocontrol (i) the reflection/transmission phase, (ii) thereflection/transmission amplitude, or (iii) the reflection/transmissionphase and the reflection/transmission amplitude. Accordingly, any of awide variety of metasurfaces may be utilized in any of the embodimentsdescribed herein that operate to control the complex phase and/orcomplex amplitude of the reflected or transmitted optical radiation.Accordingly, while specific examples are described and illustratedherein, it is understood that the various embodiments may be modified oradapted for use with alternative embodiments of optical metasurfaces andare not limited to the specifically described and illustrated examples.

According to various embodiments, an optical radiation transmissionsystem for use in a LiDAR or other sensing system may include an opticalradiation source to generate optical radiation. For example, the opticaltransmission system may include one or more lasers, a one-dimensionalarray of lasers, or a two-dimensional array of lasers. For example, thesystem may include multiple vertical-cavity surface-emitting lasers(VCSELs) suitably described as a plurality, set, array, or group ofVCSELs. In other embodiments, the system may include a plurality, set,array, and/or group of edge emitter lasers.

The system may further include a tunable optical metasurface to transmitincident optical radiation as output optical radiation that isselectively steerable in at least one steering direction within asteering range. The steering range may be, for example, a range ofangles between a first steering angle and a second steering angle, suchas −90 and +90 degrees or −120 and +120 degrees. As described herein,the tunable optical metasurface may be a transmissive-type metasurfaceor a reflective-type metasurface and may be used to steer opticalradiation and/or implement additional optical manipulation functionssuch as focusing, diverging, collimating, or otherwise beamforming theoptical radiation.

An optical assembly, including one or more optical elements, may be usedto modify the beam shape, focus, collimation, polarization, and/or otheroptical characteristics of the optical radiation generated by theoptical radiation source, and direct the modified optical radiation forincidence on the tunable optical metasurface for beam steering. In someof the examples described herein, a prism is positioned relative to thetunable optical metasurface to deflect the optical radiation generatedby the optical radiation source for incidence on the metasurface.

In various examples, the prism deflects the optical radiation generatedby the optical radiation source onto the metasurface at an angle ofincidence that is between the first steering angle and the secondsteering angle, such that the optical radiation incident on themetasurface and the steered output optical radiation from themetasurface spatially overlap within the prism for at least somesteering angles. In such embodiments, the optical radiation source maybe positioned outside of a transmission aperture of the metasurface(e.g., between the most negative and most positive steering angles), butthe optical radiation may still be directed for incidence onto themetasurface at an angle of incidence within the steering range. As such,the transmitted optical radiation and the incident optical radiationshare the transmission aperture for at least some steering angles of themetasurface without the optical source blocking the transmitted opticalradiation.

As described herein, at least one facet of the prism reflects opticalradiation from the optical radiation source that is incident on the faceat an angle greater than a critical angle for internal reflection ontothe metasurface, while simultaneously transmitting (e.g., refracting)steered optical radiation from the metasurface that passes through thesame face of the prism at an angle less than the critical angle forinternal reflection. As described and illustrated herein, the use of aprism with such a configuration and positioning relative to the opticalradiation source and the metasurface allows for the optical radiationsource to be positioned much closer to the metasurface without blockingthe steering aperture while still directing the incident opticalradiation onto the metasurface at a relatively high angle of incidencefor efficient steering thereof.

According to various embodiments, the difference between the indices ofrefraction of the prism and free space (e.g., a fluid, such as air, agas, a liquid, or empty space) results in the steered optical radiationbeing further refracted into the far-field. That is, the prism mayfurther operate to deflect the steered output optical radiation betweena first transmit angle and a second transmit angle, wherein thedifference between the first transmit angle and the second transmitangle is greater than the difference between the first steering angleand the second steering angle defining the steering range of themetasurface. As an example, the metasurface may steer the opticalradiation between −90 degrees and 90 degrees in the prism. At extremesteering angles, the prism may further refract the steered opticalradiation by an additional 30 degrees, such that the transmittedsteering angle range of the optical system extends from −120 degrees to120 degrees.

In some examples, the optical assembly may include (in addition to oralternative to a prism) one or more optical lenses, optical mirrors,polarization gratings, polarizing beam splitter elements (e.g., beamsplitter plates or cubes), half-wave plates, quarter-wave plates, and/orcombinations thereof. In some embodiments, the prism may operate toimplement additional modifications to the optical radiation generated bythe optical source prior to incidence on the metasurface and/or to thesteered optical radiation transmitted by the tuned metasurface. Forexample, the prism may be configured to additionally collimate and/ormodify a polarization state of at least some of the optical radiationgenerated by the optical radiation source prior to incidence on themetasurface. In some embodiments, modifications to the polarizationstates of the optical radiation may be performed by optical devices(e.g., waveplates, gratings, etc.) between the prism and the opticalradiation source and/or integrated into or attached to one or more facesof the prism.

The optical transmission system may include an integrated or externallyconnected controller that may be implemented as an applicant-specificintegrated circuit (ASIC), via programmable logic, as a microprocessor,as a microcontroller, as a field-programmable gate array (FPGA) oranother combination of hardware and/or software.

The controller of the optical transmission system may be configured tocause the optical radiation source to generate optical radiation andtune the metasurface to deflect incident optical radiation as outputoptical radiation steered at a target steering angle between the firststeering angle and the second steering angle.

In some embodiments, the tunable optical metasurface may be aone-dimensionally steerable metasurface that steers the opticalradiation between the first steering angle and the second steering anglealong one axis (e.g., referred to as an “azimuth axis” herein,regardless of the orientation of the system). The optical radiation inthe far-field is a transmit scan line having a narrow width along theazimuth axis and a height in the elevation axis (perpendicular to theazimuth axis in the far-field).

The height in the elevation axis of a transmitted scan line of steeredoptical radiation can be influenced by diverging optical elements (e.g.,traditional lenses, lenslet arrays, diffusers, free form optics, etc.)to diffuse transmitted optical radiation in the elevation axis and theangle of incidence of the optical radiation from the optical radiationsource in the axis corresponding to the elevation axis after deflection(e.g., reflection or refraction) by the metasurface.

Accordingly, as described herein, the system may utilize a set of VCSELsas the optical radiation source that includes a first subset of VCSELsthat can be activated to generate optical radiation for incidence on thetuned metasurface at a first angle of incidence for unsteered deflectionby the metasurface at a first elevation angle. The set of VCSELs mayinclude a second subset of VCSELs that can be activated to generateoptical radiation for incidence on the tuned metasurface at a secondangle of incidence for unsteered deflection by the metasurface at asecond elevation angle. Any number of different subsets of the VCSELscan be selectively activated to generate optical radiation for incidenceon the tuned metasurface at varying angles of incidence for unsteereddeflection by the metasurface at various, corresponding elevationangles.

In such embodiments, the metasurface steers the incident opticalradiation along the azimuth axis, and optical elements may cause thetransmitted optical radiation to diffuse or diverge along the elevationaxis. For example, the transmitter or optical transmission system mayinclude a field-of-view optical assembly to expand the field of view inthe elevation axis by diffusing or diverging the optical radiation alongthe elevation axis. Even in such embodiments, the center transmissionangle along the elevation axis and the total height of the transmittedscan line along the elevation axis can be at least partially controlledby the selective activation of different subsets of the VCSELs. In suchembodiments, the optical transmission system allows for steering of theoptical radiation in one direction via a one-dimensionally steerabletunable optical metasurface. The optical transmission system allows forquasi or effective steering of the optical radiation in the other,orthogonal direction via the selective application of different subsets,rows, or offset rows of VCSELs in an array of VCSELs.

In these embodiments, the controller of the optical transmission systemmay be configured to activate one or more subsets, rows, or groups ofVCSELs to generate optical radiation for divergence along a targetelevation angle. The controller may further tune the one-dimensionallysteerable metasurface to deflect the incident optical radiation asoutput optical radiation steered at a target steering angle.

Some of the infrastructure that can be used with embodiments disclosedherein is already available, such as general-purpose computers, computerprogramming tools and techniques, digital storage media, andcommunication links. Many of the systems, subsystems, modules,components, and the like that are described herein may be implemented ashardware, firmware, and/or software. Various systems, subsystems,modules, and components are described in terms of the function(s) theyperform because such a wide variety of possible implementations exist.For example, it is appreciated that many existing programming languages,hardware devices, frequency bands, circuits, software platforms,networking infrastructures, and/or data stores may be utilized alone orin combination to implement a specific control function.

It is also appreciated that two or more of the elements, devices,systems, subsystems, components, modules, etc. that are described hereinmay be combined as a single element, device, system, subsystem, module,or component. Moreover, many of the elements, devices, systems,subsystems, components, and modules may be duplicated or further dividedinto discrete elements, devices, systems, subsystems, components, ormodules to perform subtasks of those described herein. Any of theembodiments described herein may be combined with any combination ofother embodiments described herein.

To the extent used herein, a computing device, system, subsystem,module, driver, or controller may include a processor, such as amicroprocessor, a microcontroller, logic circuitry, or the like. Aprocessor may include one or more special-purpose processing devices,such as application-specific integrated circuits (ASICs), programmablearray logic (PAL), programmable logic array (PLA), a programmable logicdevice (PLD), field-programmable gate array (FPGA), or othercustomizable and/or programmable device. The computing device may alsoinclude a machine-readable storage device, such as non-volatile memory,static RAM, dynamic RAM, ROM, CD-ROM, disk, tape, magnetic, optical,flash memory, or another machine-readable storage medium. Variousaspects of certain embodiments may be implemented or enhanced usinghardware, software, firmware, or a combination thereof.

The components of some of the disclosed embodiments are described andillustrated in the figures herein to provide specific examples. Manyportions thereof could be arranged and designed in a wide variety ofdifferent configurations. Furthermore, the features, structures, andoperations associated with one embodiment may be applied to or combinedwith the features, structures, or operations described in conjunctionwith another embodiment. In many instances, well-known structures,materials, or operations are not shown or described in detail to avoidobscuring aspects of this disclosure. The right to add any describedembodiment or feature to any one of the figures and/or as a new figureis explicitly reserved.

The embodiments of the systems and methods provided within thisdisclosure are not intended to limit the scope of the disclosure but aremerely representative of possible embodiments. In addition, the steps ofa method do not necessarily need to be executed in any specific order,or even sequentially, nor do the steps need to be executed only once. Aspreviously noted, descriptions and variations described in terms oftransmitters are equally applicable to receivers, and vice versa.

FIG. 1 illustrates an example of a tunable liquid crystal metasurface(LCM) 100, according to one embodiment. The tunable LCM 100 can, forexample, be used as part of a solid-state optical transmitter system,receiver system, or transceiver system. As illustrated, the tunable LCM100 includes an optically reflective substrate 190 and a dielectriclayer 195. A plurality of elongated rails 191 are arranged atsub-wavelength intervals on the optically reflective substrate 190 andelectrically separated by the dielectric layer 195. The elongated rails191 may be referred to herein as “resonator rails” because the gapsbetween them (filled with liquid crystal or other dielectrics that canbe tuned to adjust a refractive index thereof) are resonant within theoptical operational bandwidth of the LCM 100. Liquid crystal or anotherrefractive index tunable dielectric material 193 is positioned betweenthe elongated rails 191. A controller or metasurface driver (notillustrated) may apply voltage differential bias patterns to theelongated rails 191 to modify a reflection phase of the resonator (ortransmission phase of the resonator in transmissive designs). Thecombination of phase delays imparted from all the resonators createsconstructive interference in a desired beam steering direction.

Additional descriptions, variations, functionalities, and usages foroptical metasurfaces are described in U.S. Pat. No. 10,451,800 grantedon Oct. 22, 2019, entitled “Plasmonic Surface-Scattering Elements andMetasurfaces for Optical Beam Steering;” U.S. Pat. No. 10,665,953granted on May 26, 2020, entitled “Tunable Liquid Crystal Metasurfaces;”and U.S. Pat. No. 11,092,675 granted on Aug. 17, 2021, entitled “LiDARSystems based on Tunable Optical Metasurfaces,” each of which is herebyincorporated by reference in its entirety. Many of the metasurfacesdescribed in the above-identified U.S. patents include parallel railspositioned above a two-dimensional or planar reflective surface orlayer.

FIG. 2A illustrates a side view of the optical path of a transmitter ofa solid-state LiDAR system 200, according to one embodiment. Aspreviously described, one or more diodes (such as laser diode array 206)generate optical radiation 230 that passes through collimating optics204 as collimated optical radiation 228. The collimated opticalradiation 228 is reflected by a transmit metasurface 210 as transmittedoptical radiation 226. According to the illustrated embodiment, thetransmitted optical radiation 226 is steered along an azimuth axis at anangle, φ. As is generally understood in the concept of LiDAR detectionsystems, the transmitted optical radiation 226 may rebound off one ormore distant objects and return as rebounded optical radiation to bedetected and measured by a detection system.

FIG. 2B illustrates a top view of an example optical path of thetransmitter of the solid-state LiDAR system 200 of FIG. 2A. One or moreoptical sources (e.g., an array of diodes 206, as illustrated) transmitsoptical radiation through collimating optics 204 to the transmitmetasurface 210. Specifically, the optical radiation from the array ofdiodes 206 is collimated by collimating optics 204 to a transmitaperture region 211 on the transmit metasurface 210.

FIG. 3 illustrates a block diagram of a transmit metasurface 316 thatreceives optical radiation 313 at a first angle of incidence, (pin, froma laser 312. The transmit metasurface 316 can be reconfigured or tuned(e.g., by a voltage controller) to transmit beamformed optical radiation313 at a target steering angle (e.g., one of the steering angles 317a-d).

FIG. 4A illustrates an array of vertically aligned rows ofvertical-cavity surface-emitting lasers (VCSELs) 400, according to oneembodiment. VCSELs emit light perpendicular to the surface of thesubstrate and tens, hundreds, or thousands of VCSELs may be arranged inrows and columns on a single chip for use as an optical radiation sourcein many of the embodiments described herein. Individual or groups ofVCSELs may be selectively activated to control the total power outputand/or angle at which the optical radiation is incident on themetasurface. In some embodiments, a controller can individually addressand selectively activate each VCSEL, groups of VCSELs, rows of VCSELs,columns of VCSELs, and/or tiles or subsets of VCSELs.

FIG. 4B illustrates an example of an array of offset rows of VCSELs 410,according to one embodiment. As previously described, the controller mayselectively activate individual groups, rows, columns, or tiles ofVCSELs. For example, each of a plurality of tiles of VCSELs may beindividually activated and deactivated by the controller. Each tile maybe defined by, for example, an N×M array of VCSELs, where N is aninteger number of rows of VCSELs and M is an integer number of columnsof VCSELs.

FIG. 5 illustrates an example of edge emitter light sources 520,according to one embodiment. Edge emitter light sources 520 may be usedas the optical radiation source in many of the embodiments describedherein.

FIG. 6A illustrates an array of VCSEL sources 600 arranged with bondpads 610 for electrical connection to a controller, according to oneembodiment. Example dimensions of 144 rows of VCSELs are provided with20-micrometer on-center spacing. Three columns of VCSELs may beapproximately 60 micrometers wide with bond pads 610 positioned onalternating sides of the array for every other row of VCSELs, such thateach row of VCSELs is individually addressable by a controller. Theexact on-center spacing, the number columns of VCSELs, and/or the widthof the columns of VCSELs may vary based on the specific implementation.

FIG. 6B illustrates another example of an array of VCSEL sources 620with offset rows, according to one embodiment. Again, bond pads 630 maybe arranged on alternating sides of the array for every other row ofVCSELs. In the illustrated example, each row of VCSELs includes 4VCSELs, and the array includes 100 rows of VCSELs. In alternativeembodiments, the optical radiation source may include any number ofVCSELs in an N×M array of vertically aligned or vertically offset rows,where N and M are arbitrary integer values.

FIG. 6C illustrates an optical transmission system 650, according to oneembodiment, that includes a tunable optical metasurface 675 to steerincident optical radiation 658 from an array of VCSEL sources on aprinted circuit board 655, according to one embodiment. In theillustrated embodiment, the VCSEL sources on the printed circuit board655 generate optical radiation 656 that is collimated by an opticalassembly 660 and 665 as collimated optical radiation 657. The opticalassembly 660 and 665 may, for example, include a rotationally symmetricaspherical lens 665 and/or a polarization grating 660. The collimatedoptical radiation 657 is reflected by a reflective optical element 670(which may be a polarization beamsplitter in some embodiments) forincidence on the metasurface 675.

As described herein, the metasurface 675 may be a voltage-controlled,tunable optical metasurface configured to be tuned for one-dimensionalsteering of the incident optical radiation 658 as transmitted opticalradiation 659. The transmitted optical radiation 659 is steered alongthe azimuth axis, denoted by cp. As an example, the VCSEL opticalradiation source on the printed circuit board 655 may include 20 rows ofVCSELs that can be selectively activated and deactivated.

FIG. 6D illustrates examples of far-field illumination via full andpartial activation of rows of VCSEL sources and different steeringangles, according to one embodiment. The far-field is represented by theregion 680. A controller (e.g., integrated within the printed circuitboard 655) may tune the metasurface 675 to steer incident opticalradiation 658 from all 20 rows of activated VCSELs at a steering angleφ1 to form an illumination pattern 685 in the far-field 680 that has afull elevation height along the height axis, denoted by θ. At adifferent time, the controller may tune the metasurface 675 to scan fromsteering angles φ2-φ5 with only rows 3-9 of the array of VCSELsactivated to reduce the elevation height of the transmitted opticalradiation to illuminate the region 687 in the far-field 680.

FIG. 7A illustrates an example of partial elevation illumination ofsteered optical radiation by partial activation of a VCSEL array 706,according to one embodiment. In the illustrated example, top rows of theVCSEL array 706 are activated to generate optical radiation incident ona metasurface 711 tuned to steer a first transmitted scan line 788 at afirst steering angle, φ1, into the far-field of a region 795. An angleof illumination along an elevation axis, θ, of the first scan line 788corresponds to the dynamically activated rows of the VCSEL array 706.The angle of illumination along the elevation axis, θ, is also affectedby static optical characteristics of lenses, lenslet arrays, prisms,diffusers, field-of-view expanders, and the like that deflecttransmitted optical radiation along the elevation axis, θ, after beingsteered by the metasurface 711.

In LiDAR systems, the first scan line 788 at the first steering angle,φ1, illuminates objects in the far-field 795 that reflect or rebound atleast some of the transmitted optical radiation to be received by areceiver subsystem (not shown). A LiDAR controller (not pictured) mayperform time-of-flight calculations (e.g., indirect and/or directtime-of-flight calculations) based on the time the first scan line 788is transmitted and when reflected/rebounded optical radiation isreceived by a sensor of the receiver system. The LiDAR controller usesthe time-of-flight calculations to calculate or otherwise determine thedistance to objects that reflected/rebounded the optical radiation ofthe first scan line 788. A LiDAR imaging system may generate an image ofobjects in the far field by combining the time-of-flight rangeinformation to each object in the far-field.

As illustrated, the LiDAR controller may then tune the metasurface 711to steer a second transmitted scan line 789 at a second steering angle,φ2, with only the upper rows of the VCSEL array 706 activated again. Theprocess can be repeated for any number of steering angles along theazimuth axis. A target resolution in the azimuth axis can be attained byadjusting the width of each scan line and the number of scan lineswithin a given region. A target resolution in the elevation axis can beattained by using a sensor with a suitable number of optical detectorsalong the elevation axis. For a given number of sensor or detectorelements, the resolution in the elevation axis can be increased byactivating a different subset of the rows of the VCSEL array 706 at thefirst and second steering angles (e.g., to illuminate a lower portion(s)of the region 795 at the same steering angles).

As depicted and described in FIGS. 7B-7D below, various combinations ofsteering angles along the steering axis can be attained by tuning themetasurface 711. Similarly, various combinations of effective steeringangles are possible along the elevation axis by selectively activatingdifferent rows of the VCSEL array 706. The refresh rate of LiDAR imagingis based, at least in part, on the time it takes for the scan lines toscan a region of interest in the far-field along both the steering axis(by tuning the metasurface) and the elevation axis (by selectiveactivation of different rows of the VCSEL array 706).

FIG. 7B illustrates another example of partial elevation illumination ofsteered optical radiation by activation of a different subset of theVCSEL array 706, according to one embodiment. As illustrated, acontroller tunes the metasurface 711 to steer optical radiation 791 and792 at steering angles φ3 and φ4 with a middle subset of the VCSEL array706 activated (shown with shading).

FIG. 7C illustrates another example of partial elevation illumination ofsteered optical radiation by activation of a different subset of theVCSEL array 706, according to one embodiment. As illustrated, acontroller tunes the metasurface 711 to steer optical radiation 793 and794 at steering angles φ5 and φ6 with a lower subset of the VCSEL array706 activated (shown with shading).

FIG. 7D illustrates an example of complete elevation illumination ofsteered optical radiation by activation of the entire VCSEL array 706,according to one embodiment. As illustrated, a controller tunes themetasurface 711 to steer optical radiation 796 and 797 at steeringangles φ7 and φ8 with a lower subset of the VCSEL array 706 activated(shown with shading).

Many implementations of tunable optical metasurfaces operate to steeroptical radiation with a single linear polarization. That is, opticalradiation that does not have the correct linear polarization is notsteered by the tunable optical metamaterial. Accordingly, a commonapproach is to use a polarization filter that passes only the opticalradiation having the correct linear polarization for incidence on thetunable optical metamaterial. However, this results in optical lossesand a reduction in power efficiency in terms of the power used togenerate a given optical transmission. Some of the embodiments of thepresently described systems and methods propose optical assemblies tocovert all of the optical radiation to the correct polarization forsteering by the tunable optical metasurface.

FIG. 8 illustrates an example of an optical assembly for polarizationspatial combining of optical radiation 891 from an unpolarized source801, according to one embodiment. In the illustrated embodiment, theunpolarized optical radiation source 801 (e.g., on a printed circuitboard) generates optical radiation 891 that is collimated by a lens 805to form collimated optical radiation 892. The collimated opticalradiation 892 is reflected by a combiner (polarization prism 811 andrhomboid 810) with a half-wave plate 812.

For example, a thin-film coating on the hypotenuse of the polarizationprism 811 splits the collimated optical radiation into a first beam witha first linear polarization traveling in a first direction and a secondbeam with a second linear polarization orthogonal to the first linearpolarization traveling in a second direction. The half-wave plate 812rotates the polarization of the first beam to be the same as the linearpolarization of the second beam. A rhomboid 810 is positioned on thehypotenuse face of the polarization prism 811 to deflect the second beamto travel in the same direction as the first beam. As illustrated, thepolarization prism 811, half-wave plate 812, and the rhomboid 810operate to linearly polarize the optical radiation generated by theunpolarized source 801 with minimal optical losses.

FIG. 9 illustrates another example of an optical assembly forpolarization spatial combining of optical radiation 991 from anunpolarized source 901, according to one embodiment. Again, the opticalradiation 991 is collimated by a lens 905 and reflected by a polarizingbeam splitter plate 910. One of the split beams 994 is passed through ahalf-wave plate 920 and the other split beam 993 is not.

FIG. 10 illustrates another example of an optical assembly forpolarization spatial combining of optical radiation 1091 from anunpolarized source 1001, according to one embodiment. The opticalradiation 1091 is collimated by a lens 1005 with random polarization.The collimated optical radiation 1092 passes through a polarizationgrating 1010 to generate optical radiation 1093 with right-handedcircular polarization and optical radiation 1094 with left-handedcircular polarization. The optical radiation 1093 is passed through aquarter-wave plate 1020 with a first clocking position (e.g., −45degrees) to generate linearly polarized optical radiation 1095. Theoptical radiation 1094 is passed through a quarter-wave plate 1030 witha second clocking position that is 90 degrees out of phase with thefirst clocking position (e.g., +45 degrees) to generate linearlypolarized optical radiation 1096.

FIG. 11 illustrates another example of an optical assembly forpolarization spatial combining of optical radiation 1191 with randompolarization from an unpolarized source 1101, according to oneembodiment. In the illustrated embodiment, the optical radiation 1191passes through a polarization grating 1110 before each beam 1192 and1193 is collimated by a lens assembly 1105 as collimated opticalradiation 1194 and 1195 with right-handed circular polarization andleft-handed circular polarization, respectively. The beams of opticalradiation 1194 and 1195 are passed through quarter-wave plates 1120 and1130, respectively, to generate linearly polarized optical radiation1196 and 1197, respectively. As in FIG. 10 , the quarter-wave plates1120 and 1130 may be on the same substrate with −45-degree and+45-degree clocking positions.

FIG. 12A illustrates two beams (using different dashed lines) overlaidin the same plane using a half-wave plate 1205 for an S-pol beam paththrough a prism 1275 to a metasurface 1250 for reflection at a targetsteering angle, according to one embodiment. The optical radiation maybe collimated, combined, and polarized via one or more lenses 1201,half-wave plate 1205, and a polarization beam splitter cube and/or prismassembly 1207 (e.g., three prisms or a cube).

As illustrated, the prism 1275 comprises a lower planar face that sitson top of the metasurface and an upper planar face 1217. The lowerplanar face and the upper planar face 1217 are parallel to one another.Many variations of prisms are described herein that show opticalradiation being transmitted from an optical radiation source through aprism for transmission and steering by a tunable optical metasurface.However, it is appreciated that the illustrated embodiments of prismsand tunable optical metasurfaces can be used in reverse to receiveoptical radiation at a target steering angle and transmit the receivedoptical radiation through the prism to a sensor (e.g., an array of diodesensors).

FIG. 12B illustrates a bottom view of the optical radiation directedthrough the collimating lens, prism(s), polarizing beam splitterelement, and half-wave plate (1201, 1203, 1205, and 1207) prior to beingdirected into the coupling prism of the metasurface, according to oneembodiment.

FIG. 12C illustrates a side view of optical radiation from an opticalradiation source on a printed circuit board 1250 collimated by a lens1201. The collimated optical radiation is passed through a polarizationbeam splitter element and prism assembly 1203 and a half-wave plate 1205before entering a lateral face of the coupling prism 1275. The opticalradiation is incident on the lateral face of the coupling prism 1275 atan angle for refraction into the coupling prism 1275. The opticalradiation is refracted within the coupling prism 1275 at an angle forinternal reflection on the upper face of the prism toward a metasurface1280 at a target angle of incidence.

The polarization beam splitter element and prism assembly 1203 operateto split the collimated optical radiation into a first beam and a secondbeam. One of the beams is passed through the half-wave plate 1205 suchthat both beams have the same linear polarization suitable for incidenceon and steering by the tunable optical metasurface 1280.

As illustrated, the optical radiation is incident on the metasurface1280 at a high angle of incidence (e.g., less than 45 degrees). Such ahigh angle of incidence is not possible in embodiments without acoupling prism 1275 without the optical radiation source or otheroptical elements blocking at least a portion of the steering aperture ofthe metasurface 1280. The metasurface 1280 is tunable to steer incidentoptical radiation for transmission between a first steering angle and asecond steering angle (e.g., within a steering range) along a steeringaxis (e.g., again, referred to herein as the azimuth axis).

As illustrated, the coupling prism 1275 includes a lateral face 1218that extends from an edge of the lower face 1219 of the coupling prism1275 at an obtuse angle to an edge of the upper face 1217 of thecoupling prism 1275. The linearly polarized and collimated opticalradiation is transmitted through the lateral face 1218 (and refractedupon entry) at an angle for internal reflection by the upper surface1217 of the prism coupling prism for incidence on the tunable opticalmetasurface 1280.

FIG. 12D illustrates a side view of the optical radiation transmissionsystem 1200 steered to a second steering angle, according to oneembodiment. As illustrated, optical radiation is steered at a steeringangle, φ, by the metasurface 1280. As the optical radiation leaves thecoupling prism 1275, the optical radiation is refracted for transmissionat a transmit steering angle, φ+, that is greater than the originalsteering angle, φ.

FIG. 12E illustrates the side view of the optical radiation transmissionsystem 1200 steered to a third steering angle at which the transmittedoptical radiation overlaps the incoming optical radiation from anoptical source that is incident on the metasurface 1280, according toone embodiment. Again, the configuration and positioning of the couplingprism 1275 allow the incident optical radiation and the transmittedoptical radiation to travel within a shared aperture without the opticalradiation source (or associated mirrors or lens) blocking a portion ofthe aperture.

As illustrated, the metasurface 1280 steers the optical radiation at asteering angle, −φ. As the optical radiation leaves the coupling prism1275, the optical radiation is refracted for transmission at a transmitsteering angle, −φ−, that exceeds the original steering angle, φ−.Notably, the optical radiation 1298 that is internally reflected by theupper surface of the prism for incidence on the metasurface 1280 isincident on the internal surface of the prism at an angle greater thanthe critical angle of the prism 1275 such that it is reflected. Incontrast, the optical radiation steered by the metasurface 1280 isincident on the internal surface of the prism 1275 at an angle less thanthe critical angle, such that the steered optical radiation is refractedout of the prism 1275 at the transmit steering angle.

FIG. 13A illustrates example components of an optical assembly 1375similar to the optical assembly described in conjunction with FIGS. 12Aand 12B, according to various embodiments. As illustrated, the opticalassembly 1375 includes a half-wave plate 1371, a polarizing beamsplitter element 1372, a large right-angle prism 1374, and an outputright-angle prism 1373. In various embodiments, the large right-angleprism 1374 may be formed as a single element or as two elements joinedtogether.

FIG. 13B illustrates the optical path through the optical prism assembly1375, according to one embodiment.

FIGS. 14A-D illustrate example views of a transmissive (e.g.,refractive-type) metasurface 1480 with a half-wave plate 1425, accordingto various embodiments. As illustrated, optical radiation 1491 iscollimated by a toroidal lens 1410 and steered by the refractive-typemetasurface 1480 as optical radiation 1493 and 1494. The opticalradiation 1494 is passed through a half-wave plate 1425.

FIGS. 15A-D illustrate example views of a reflective metasurface 1580with a half-wave plate 1585, according to various embodiments. Asillustrated, optical radiation 1591 is collimated by a toroidal lens1510. Optical radiation 1594 with S-polarization is reflected throughthe half-wave plate 1585. Optical radiation 1593 with P-polarization isdiffracted by the metasurface 1580.

FIGS. 16A-B illustrate examples of metasurface transmitters utilizinglow-angle optical assemblies to convey optical radiation to ametasurface 1680, according to various embodiments. In each of FIGS. 16Aand 16B, optical radiation from an optical radiation source is steeredthrough optical assembly elements 1605, 1610, 1620, and 1625 forincidence on the metasurface 1680 at a relatively low angle ofincidence. The metasurface 1680 steers the optical radiation within asteering range. The optical radiation incident on the metasurface 1680from the optical assembly elements 1605, 1610, 1620, and 1625 isincident at a relatively low angle such that the optical assemblyelements do not block the steered optical radiation transmitted by themetasurface 1680.

FIG. 16C illustrates an example of a metasurface transmitter with adiffuser 167 to diffuse unsteered optical radiation 1695, according toone embodiment. Most of the incident optical radiation 1690 is steeredby the metasurface 1680 as steered beam 1693. In a perfectly efficientsystem, all the incident optical radiation 1690 is steered by themetasurface 1680. However, in many actual implementations, some of theincident optical radiation 1690 is reflected as unsteered opticalradiation 1695. In the illustrated embodiment, a diffuser 1697 ispositioned to receive the unsteered optical radiation 1695 and diffusethe unsteered optical radiation 1695 and diffuse it as diffuse radiation1699. The diffuser 1697 may be, for example, an opal plate, frostedgrass, an engineered diffuser, an etching, etc.

In lidar systems, the diffuser may operate to illuminate objects locatedat short range to increase the effective dynamic range of the lidarsystem. As previously described, in a lidar system, the steered opticalradiation 1693 illuminates objects at short, medium, and long range. Theobjects reflect a portion of the steered optical radiation 1693 back toa lidar receiver. The intensity of the received optical radiationgenerally decreases as the distance to the object increases. As such,the optical radiation received from objects at medium and long range isgenerally less intense than the optical radiation received at shortrange. In fact, at short range, the optical radiation reflected by theobject to be received by the lidar receiver may be more than desirableand outside of the dynamic range of the lidar receiver sensors. Thediffuser 1697 operates to uniformly or quasi-uniformly illuminateobjects at short range so as to decrease the dynamic range of the sceneat short range.

FIGS. 17A-24 illustrate examples of optical transmitters utilizingprisms to convey optical radiation to a tunable metasurface from opticalradiation sources in various locations relative to the metasurface,according to various embodiments.

FIG. 17A illustrates an optical radiation transmission system 1700 withoptical elements 1705, 1725, and 1727 for collimating and polarizingoptical radiation from an optical radiation source on a printed circuitboard 1770. The collimated and polarized optical radiation enters afirst surface of a coupling prism 1775 and is reflected off a mirror1776 (e.g., a mirrored surface of the coupling prism 1775) toward anupper surface of the coupling prism 1775. The optical radiation isincident on the upper surface of the coupling prism 1775 at an anglegreater than the critical angle and is reflected downward for incidenceon the metasurface 1780. In the illustrated example, the opticalassembly for collimating and polarizing includes a lens 1705, apolarizing beam splitter plate 1725, and a half-wave plate 1727. Theangle of the mirrored surface 1776 can be selected to achieve a targetangle of incidence on the metasurface 1780 to affect the orders to beused for steering.

FIG. 17B illustrates the optical radiation transmission system 1700 ofFIG. 17A with a sensor 1798 (e.g., a photodetector, photodiode,processor, memory, data communication circuitry, and/or the like) todetect unsteered optical radiation 1795, according to one embodiment. Aspreviously described, most of the incident optical radiation 1790 thatis incident on the metasurface 1780 is steered through the prism 1775 assteered optical radiation 1793. However, due to system and componentinefficiencies, some of the incident optical radiation 1790 is reflectedby the metasurface 1780 as unsteered optical radiation 1795. The path ofthe unsteered optical radiation 1795 is illustrated with darker shadingas it is reflected off the upper surface of the prism 1775. One beam isreceived by the sensor 1798 after reflecting off the upper surface ofthe prism 1775. The other beam is received by the sensor 1798 afterreflecting off the upper surface of the prism 1775 and the vertical,left wall of the prism 1775.

According to various embodiments, the sensor 1798 may be used to detectthe laser power being generated. For example, if the metasurface 1780steers incident optical radiation 1790 with 95% efficiency, the sensor1798 can be expected to detect approximately 5% of the power generatedby the laser. In another implementation, the power output of the laseror LED may be known and the sensor 1798 can be used to measure thesteering efficiency of the metasurface 1780. That is, if 2% of theoptical radiation generated by the laser or LED source is received bythe sensor, the metasurface can be estimated at approximately 98%efficient, less any known or estimated losses in the various opticalelements 1705, 1725, and 1727, the prism 1775, and the mirrored surface1776.

In some embodiments, the metasurface 1780 may be tuned off so the sensor1798 can be used to measure the intensity of the LED or laser. Themetasurface may then be turned on to measure the efficiency of themetasurface at different steering angles or an average efficiency acrossall steering angles.

In some embodiments, a metasurface efficiency and/or power output of anoptical radiation source may be measured as part of a factorycalibration, manufacturing, or setup. The efficiency and/or powerintensity may be measured at later dates to confirm the health andcontinued operation of the metasurface and/or optical radiation source(e.g., LED or laser). In some embodiments, the sensor 1798 may be usedto measure the switching speed of the metasurface 1780 as themetasurface 1780 is used to steer the optical radiation at differentsteering angles. In some embodiments, the sensor 1798 may be used toensure that the output optical radiation steered by the metasurface 1780does not exceed operational rules, safety standards, or eye safetystandards.

FIG. 18A illustrates an optical radiation transmission system 1800 witha collimating lens 1805 and a polarization grating 1827 for collimatingand polarizing optical radiation from an optical radiation source 1801on a printed circuit board 1870. The collimated and polarized opticalradiation enters an input facet 1876 of a coupling prism 1875 and isrefracted for internal reflection by an upper surface of the couplingprism 1875 for incidence on a metasurface 1880. Two quarter-wave plates1832 are positioned adjacent to one another (e.g., coplanar and side byside) between the coupling prism 1875 and the metasurface 1880, suchthat the optical radiation passes through one of the quarter-wave plate1832 before incidence on the metasurface 1880 and after being steeredfor transmission by the metasurface 1880. The input facet 1876 of thecoupling prism 1875 has a Brewster angle that does not need to becoated. Stray light can be rejected on the opposite facet.

FIG. 18B illustrates another view of the optical radiation transmissionsystem 1800 showing the spatial separation of the differentpolarizations of optical radiation, according to one embodiment. Asillustrated, optical radiation is passed through a polarization gratingto effectuate spatial separation of the optical radiation with circularright polarization 1890 a and optical radiation with circular leftpolarization 1890 b. The two quarter-wave plates 1832 a and 1832 blinearly polarize the optical radiation 1893 a and 1893 b, which issteered by the metasurface.

FIG. 18C illustrates the optical radiation transmission system 1800 witha diffuser 1897 to diffuse unsteered optical radiation 1895. While ahigh percentage of the incident optical radiation 1890 is steered by themetasurface 1880 as steered beam 1893. However, a small percentage ofthe incident optical radiation 1890 is reflected as unsteered opticalradiation 1895. The diffuser 1897 may be a discrete element within theprism 1875 (as illustrated), a grating or pattern etched into thesurface of the prism 1875, or as a discrete element external to theprism 1875. The diffuser 1897 receives and diffuses the unsteeredoptical radiation 1895 as diffuse radiation 1899.

FIG. 19 illustrates an optical radiation transmission system 1900 with acollimating lens 1905, a polarizing beam splitter plate 1925, and ahalf-wave plate 1927 to collimate and polarize optical radiation from anoptical radiation source on a printed circuit board 1970. The opticalradiation enters a surface of a coupling prism 1975 and is reflected byan opposing mirrored surface 1976 for incidence on a metasurface 1980.The angle of the mirrored surface 1976 can be selected to achieve atarget angle of incidence on the metasurface 1980 to affect orders to beused for steering.

In the illustrated embodiment, the first surface of the coupling prism1975 extends between the lower and upper faces of the coupling prism atright angles. The mirrored surface extends at an acute angle from thelower surface and connects to the upper surface at an obtuse angle.

FIG. 20A illustrates an optical radiation transmission system 2000 witha collimating lens 2005 and a polarization spatial combiner 2027 (prism,rhomboid, and half-wave plate) to collimate and polarize opticalradiation from an optical radiation source 2070 that is positionedorthogonal to the primary printed circuit board 2071. The opticalradiation enters an input facet 2076 of a coupling prism 2075 and isreflected by an upper surface for incidence on a metasurface 2080.Again, the input facet 2076 of the coupling prism 2075 may be configuredwith a Brewster angle that does not need to be coated and the specularlight can be rejected on the opposite facet.

FIG. 20B illustrates the optical radiation transmission system 2000 witha reflective diffuser to diffuse unsteered optical radiation, accordingto one embodiment. As illustrated, the unsteered optical radiation beams2095 are reflected out of the prism 2075 where they are received by anexternal diffuser 2097. The external diffuser 2097 may be, for example,an opal plate, frosted grass, an engineered diffuser, an etching, etc.The external diffuser 2097 reflects and diffuses the unsteered opticalradiation 2095 into the short range as diffuse radiation 2099.

FIG. 20C illustrates the optical radiation transmission system 2000 witha photodetector 2098 in the printed circuit board 2071 to detectunsteered optical radiation 2095 that is reflected by the metasurface2080 out of the prism 2075, according to one embodiment. Again, most ofthe incident optical radiation 2090 that is incident on the metasurface2080 is steered through the prism 2075 as steered optical radiation2093. Some of the incident optical radiation 2090 is reflected by themetasurface 2080 as unsteered optical radiation 2095. The path of theunsteered optical radiation 2095 is illustrated with darker shading asit is reflected off the upper surface of the prism 2075 and thendownward out of the lateral face of the prism 2075 that extends at anobtuse angle from the base of the prism 2075.

The photodetector 2098 (optionally in conjunction with other componentson the printed circuit board 2071 and/or off-chip components) is used todetect the unsteered optical radiation 2095. The measurement of theintensity of the unsteered optical radiation 2095 may be used to measurethe efficiency of the metasurface 2080, the power output of the LED orlaser optical radiation source 2070, the health of the optical radiationsource 2070 or metasurface 2080, the switching speed of the metasurface2080.

FIG. 21 illustrates an optical radiation transmission system 2100 with acollimating lens 2105, a polarizing beam splitter plate 2125, ahalf-wave plate 2127, and a right-angle prism 2129 to direct thecombined and polarized optical radiation into a trapezoidal couplingprism 2175. The optical radiation enters an input facet of the couplingprism 2175 and is reflected by an upper surface for incidence on themetasurface 2180 positioned on a printed circuit board 2170 or anothersubstrate. A diffuser 2185 may operate to diffuse the optical radiationalong an elevation axis as the optical radiation is steered along abazimuth axis by the metasurface 2180. A facet of the trapezoidalcoupling prism 2175 opposite the input facet may include a specular dump2179 to absorb, deflect, or otherwise reduce stray optical radiationwithin the prism.

FIG. 22 illustrates an optical radiation transmission system 2200 with acollimating lens 2205, a polarizing beam splitter plate 2225, ahalf-wave plate 2227, and a mirror 2229 to direct combined and polarizedoptical radiation through holes in a printed circuit board 2270 (oranother substrate) into a trapezoidal coupling prism 2275. The opticalradiation enters an input facet of the coupling prism 2275 and isreflected by an upper surface for incidence on the metasurface 2280.Again, a diffuser 2285 may operate to diffuse the optical radiationalong an elevation axis as the optical radiation is steered along anazimuth axis by the metasurface 2280. A facet of the trapezoidalcoupling prism 2275 opposite the input facet may include a specular dump2279 to absorb, deflect, or otherwise reduce or eliminate stray opticalradiation within the prism.

FIG. 23 illustrates an optical radiation transmission system 2300 with acollimating lens 2305, a polarizing beam splitter plate 2325, ahalf-wave plate 2327, and a mirror 2329 to direct the combined andpolarized optical radiation into a trapezoidal coupling prism 2375. Theoptical radiation enters an input facet of the coupling prism 2375 andis reflected by an upper surface for incidence on a metasurface 2380.Again, a diffuser 2385 may operate to diffuse the optical radiationalong an elevation axis as the optical radiation is steered along anazimuth axis by the metasurface 2380. A facet of the trapezoidalcoupling prism 2375 opposite the input facet may include a specular dump2379 to reduce stray optical radiation.

FIG. 24 illustrates an optical radiation transmission system 2400 with acollimating lens 2405, a combiner 2429 (prism and rhomboid), and ahalf-wave plate 2427 to direct the combined and polarized opticalradiation into a trapezoidal coupling prism 2475. The optical radiationenters an input facet of the coupling prism 2475 and is reflected by anupper surface for incidence on a metasurface 2480 at a much higher angleof incidence than is possible in prismless designs (without the opticalradiation source or diffracting optical elements blocking a portion ofan aperture). Again, a diffuser 2485 may operate to diffuse the opticalradiation along an elevation axis as the optical radiation is steeredalong an azimuth axis by the metasurface 2480. A facet of thetrapezoidal coupling prism 2475 opposite the input facet may include aspecular dump 2479 to absorb and/or deflect stray optical radiation.

FIGS. 25A-C illustrate a comparison of low-angle “prism less” opticalassemblies with prism-based optical assemblies at various steeringangles, according to various embodiments. The prismless layouts on thetop row illustrate optical radiation 2592 incident on a metasurface 2580at a relatively low angle before being steered as transmitted opticalradiation 2594 at −45 degrees, 0 degrees, and +45 degrees by themetasurface 2580. In such embodiments, the optical radiation source (notshown) is relatively far away from the metasurface 2580 as compared toembodiments utilizing prisms.

In the prism-based layouts in the bottom row of each of FIGS. 25A-C, anaperture within the prism 2575 is shared by both the incident opticalradiation 2590 directed toward the metasurface 2580 and the opticalradiation 2595 transmitted by the metasurface at the various steeringangles. The shared aperture within the prism 2575 allows for compactpackaging and relatively close spacing of the optical radiation sourceand the metasurface.

FIG. 26 illustrates an example of an optical transmitter 2600 with acoupling prism 2675 and a tunable metasurface 2680, according to oneembodiment. A VCSEL array 2601 (or alternative optical radiation source)is driven by the VCSEL driver 2602 to generate optical radiation thatpasses through a polarization grating 2685 before entering a bottomfacet of the coupling prism 2675. The optical radiation is reflected bya mirrored facet 2676 of the coupling prism that is at an angle relativeto a bottom facet and a top facet 2678 of the coupling prism 2675. Theoptical radiation is reflected over the metasurface 2680 toward amirrored collimating facet 2677 on an opposing side of the couplingprism 2675. The optical radiation is collimated by the collimating facet2677 (e.g, a mirrored face) and reflected toward the upper surface 2678of the coupling prism.

The upper surface 2678 of the coupling prism 2675 may be coated with anoptical coating to achieve a target reflection and/or refractionpattern. The collimated optical radiation is reflected by the uppersurface 2678 for incidence on the metasurface 2680 after passing througha half-wave plate 2682 and a glass cover 2681. The metasurface 2680 istuned and driven by a metasurface driver 2683 on the printed circuitboard 2670 to steer the incident optical radiation for far-fieldtransmission.

FIG. 27A illustrates another example of an optical transmitter 2700 witha coupling prism 2775, a tunable metasurface 2780, and a cylindricaldefocusing lens 2779, according to one embodiment. The opticaltransmitter 2700 is packaged within a housing 2799 positioned on aprinted circuit board 2770. A VCSEL driver 2702 drives a VCSEL array2701 (e.g., a one-dimensional or two-dimensional array of VCSELs) togenerate optical radiation. The optical radiation passes through a beamdeflector 2705 into the coupling prism 2775 for internal reflection andincidence on the metasurface 2780 (after passing through a coverglass2781). In the illustrated embodiment, the metasurface 2780 steers andcollimates the optical radiation. The cylindrical defocusing lens 2779diffuses or spreads laser light in the vertical axis (e.g., non-steeringor elevation axis).

FIG. 27B illustrates an example embodiment of a LiDAR system 2703 usingthe optical transmitter 2700 of FIG. 27A and a time-of-flight sensor2785 within a housing 2771 that secures a receiver optical assembly2786, according to one embodiment. The specific elements of the opticaltransmitter 2700 are described in conjunction with FIG. 27 above.

FIG. 28A illustrates a metasurface-based transmitter device with a lens2850 to expand optical radiation 2890 steered by a metasurface 2880 in anon-steering direction. The lens 2850 can generate a symmetrical fanbeam in the non-steering direction.

FIG. 28B illustrates a metasurface-based transmitter device with alenslet array diffuser 2851 to expand the optical radiation 2890 steeredby the metasurface 2880 in the non-steering direction. The lenslet arraydiffuser 2851 can generate a symmetrical fan beam in the non-steeringdirection.

FIG. 28C illustrates a metasurface-based transmitter device with afreeform optic diffuser 2852 to expand the optical radiation 2890steered by the metasurface 2880 in the non-steering direction. Thefreeform optic diffuser 2852 can also be configured to correctasymmetrical distortion.

FIG. 29 illustrates a range of straight and curved transmit scan lines2910 of a low-angle, “prism less” metasurface 2900 at various steeringangles, according to one embodiment. As illustrated, at negativesteering angles, the transmit scan lines 2910 are curved and may bedifficult to detect by a straight array of sensors in a LiDAR receiveror other sensor arrays. At positive steering angles, the transmit scanlines 2910 are straighter.

FIG. 30 illustrates a range of straight and curved transmit scan lines3012 of a metasurface 3000 with a prism, according to one embodiment. Asillustrated, the scan lines 3012 are straight at 0-degree steeringangles and become increasingly curved as optical radiation is steered ineither direction.

FIG. 31 illustrates a curvature of transmit scan lines 3114 in afar-field using an optical transmitter 3100 with a tunable metasurface3180, a prism 3175, and an optical FOV expander 3151 (e.g., a lensletarray diffuser), according to one embodiment. Similar to FIG. 30 , thescan lines 3114 are straight at 0-degree steering angles and becomeincreasingly curved as optical radiation is steered in either direction.

FIG. 32 illustrates an example of a receive lens 3220 with barreldistortion used to compensate for inherent pincushion distortion oftransmit scan lines 3210 such that detected optical radiation is alignedin straight lines on a sensor 3230, according to one embodiment.

This disclosure has been made with reference to various exemplaryembodiments, including the best mode. However, those skilled in the artwill recognize that changes and modifications may be made to theexemplary embodiments without departing from the scope of the presentdisclosure. While the principles of this disclosure have been shown invarious embodiments, many modifications of structure, arrangements,proportions, elements, materials, and components may be adapted for aspecific environment and/or operating requirements without departingfrom the principles and scope of this disclosure. These and otherchanges or modifications are intended to be included within the scope ofthe present disclosure.

This disclosure is to be regarded in an illustrative rather than arestrictive sense, and all such modifications are intended to beincluded within the scope thereof. Likewise, benefits, other advantages,and solutions to problems have been described above with regard tovarious embodiments. However, benefits, advantages, solutions toproblems, and any element(s) that may cause any benefit, advantage, orsolution to occur or become more pronounced are not to be construed as acritical, required, or essential feature or element. This disclosureshould, therefore, be determined to encompass at least the followingclaims and all possible permutations thereof.

The invention claimed is:
 1. A solid-state light detection and ranging(LiDAR) transmitter, comprising: a tunable optical metasurface toselectively steer incident optical radiation between a first steeringangle and a second steering angle along an azimuth axis; a plurality oflaser sources to generate optical radiation, wherein different subsetsof the plurality of laser sources are configured to be selectivelyactivated to generate optical radiation for incidence on the tunableoptical metasurface at different angles of incidence on an elevationaxis for unsteered deflection by the tunable optical metasurface atcorresponding angles of elevation; an optical assembly to collimate andlinearly polarize the optical radiation generated by the plurality oflaser sources; a prism positioned relative to the tunable opticalmetasurface to: deflect steered output optical radiation between a firsttransmit angle and a second transmit angle, wherein the differencebetween the first transmit angle and the second transmit angle isgreater than the difference between the first steering angle and thesecond steering angle, and deflect the optical radiation from theoptical assembly by an optical radiation source for incidence on thetunable optical metasurface at an angle of incidence that is between thefirst steering angle and the second steering angle, such that theoptical radiation incident on the tunable optical metasurface and thesteered output optical radiation from the tunable optical metasurfacespatially overlap within the prism for at least some steering anglesbetween the first steering angle and the second steering angle; and acontroller to: tune the tunable optical metasurface to steer incidentoptical radiation at a target azimuth angle, and activate a subset ofthe plurality of laser sources to generate optical radiation forincidence on the tuned optical metasurface at an angle of incidence forunsteered deflection by the tuned optical metasurface at a targetelevation angle.
 2. A solid-state light detection and ranging (LiDAR)system, comprising: a tunable optical metasurface to selectivelytransmit incident optical radiation between a first steering angle and asecond steering angle along an azimuth axis, wherein the tunable opticalmetasurface comprises: an array of elongated rails positioned above areflective surface, wherein the elongated rails are configured withinterelement spacings less than an operational wavelength, and arefractive index tunable dielectric material positioned in optical fieldregions between adjacent elongated rails; a plurality of laser sourcesto generate optical radiation, wherein different subsets of theplurality of laser sources are configured to be selectively activated togenerate optical radiation for incidence on the tunable opticalmetasurface at different angles of incidence on an elevation axis forunsteered deflection by the tunable optical metasurface at correspondingangles of elevation; an optical assembly to direct the optical radiationgenerated by each subset of the laser sources onto the tunable opticalmetasurface; and a controller to: identify a target azimuth angle alongthe azimuth axis and a target elevation angle along the elevation axis,tune the tunable optical metasurface to steer incident optical radiationat the target azimuth angle, and activate a subset of the laser sourcesto generate optical radiation for incidence on the tuned opticalmetasurface at an angle of incidence for unsteered deflection by thetuned optical metasurface at the target elevation angle.
 3. The systemof claim 2, wherein the subset of laser sources comprises an array ofvertical-cavity surface-emitting lasers (VCSELs).
 4. The system of claim2, wherein the subset of laser sources comprises an array of edgeemitter lasers.
 5. The system of claim 2, wherein the refractive indextunable dielectric material comprises liquid crystal.
 6. The system ofclaim 5, wherein the controller is configured to tune the tunableoptical metasurface by selectively applying different voltages to theelongated rails to generate a voltage differential bias pattern withinthe liquid crystal between the elongated rails.
 7. The system of claim2, wherein the optical assembly comprises one or more of: an opticallens, an optical mirror, a polarization grating, a polarizing beamsplitter, a half-wave plate, and a quarter-wave plate.
 8. A solid-statelight detection and ranging (LiDAR) system, comprising: a tunableoptical metasurface to selectively transmit incident optical radiationbetween a first steering angle and a second steering angle along anazimuth axis; a plurality of laser sources to generate opticalradiation, wherein different subsets of the plurality of laser sourcesare configured to be selectively activated to generate optical radiationfor incidence on the tunable optical metasurface at different angles ofincidence on an elevation axis for unsteered deflection by the tunableoptical metasurface at corresponding angles of elevation; a prismpositioned relative to the tunable optical metasurface to: direct theoptical radiation generated by each subset of the laser sources forincidence on the tunable optical metasurface at an angle of incidencethat is between the first steering angle and the second steering angle,such that the optical radiation incident on the tunable opticalmetasurface and a steered output optical radiation from the tunableoptical metasurface spatially overlaps within the prism for at leastsome steering angles between the first steering angle and the secondsteering angle, and deflect the steered output optical radiation betweena first transmit angle and a second transmit angle, wherein thedifference between the first transmit angle and the second transmitangle is greater than the difference between the first steering angleand the second steering angle; and a controller to: identify a targetazimuth angle along the azimuth axis and a target elevation angle alongthe elevation axis, tune the tunable optical metasurface to steerincident optical radiation at the target azimuth angle, and activate asubset of the laser sources to generate optical radiation for incidenceon the tuned optical metasurface at an angle of incidence for unsteereddeflection by the tuned optical metasurface at the target elevationangle.
 9. The system of claim 8, wherein the prism comprises a lowerplanar face and an upper planar face that are parallel to one another,and wherein the lower planar face of the prism is positioned above andparallel to the tunable optical metasurface, such that the outputoptical radiation steered by the tunable optical metasurface istransmitted through the lower planar face of the prism and the upperplanar face of the prism.
 10. An optical transmission system,comprising: an optical radiation source to generate unpolarized opticalradiation; an optical assembly to collimate and linearly polarize theoptical radiation; and a tunable optical metasurface to transmitincident, linearly polarized optical radiation as output opticalradiation that is selectively steerable in at least one steeringdirection within a steering range defined by a first steering angle anda second steering angle, wherein the tunable optical metasurfacecomprises: an array of elongated rails positioned above a reflectivesurface, wherein the elongated rails are configured with interelementspacings less than a wavelength of the optical radiation generated bythe plurality of laser sources; and a refractive index tunabledielectric material positioned in optical field regions between adjacentelongated rails.
 11. The system of claim 10, wherein the opticalassembly comprises one or more of: an optical lens, an optical mirror, apolarization grating, a polarizing beam splitter, a half-wave plate, anda quarter-wave plate.
 12. The system of claim 10, wherein the opticalassembly comprises: a collimating lens to collimate the unpolarizedoptical radiation; a polarizing prism to split the collimated opticalradiation into a first beam with a first linear polarization travelingin a first direction and a second beam with a second linear polarizationorthogonal to the first linear polarization traveling in a seconddirection; a half-wave plate to rotate the polarization of the firstbeam to be the same as the second linear polarization; and a rhomboidpositioned proximate to the polarization prism to redirect the secondbeam to travel in the first direction along with the first beam.
 13. Thesystem of claim 10, wherein the optical assembly comprises: acollimating lens to collimate the unpolarized optical radiation; apolarization grating to receive the collimated unpolarized opticalradiation to generate a first beam with left-handed circularpolarization and a second beam with right-handed circular polarization;a first quarter-wave plate with a first orientation to adjust thepolarization of the first beam to be linearly polarized; and a secondquarter-wave plate with a second orientation to adjust the polarizationof the second beam to be linearly polarized.
 14. The system of claim 10,wherein the optical assembly comprises: a collimating lens to collimatethe unpolarized optical radiation; a polarization beam splitter to splitthe collimated optical radiation into a first beam with a first linearpolarization traveling in a first direction and a second beam with asecond linear polarization orthogonal to the first linear polarizationtraveling in a second direction; a half-wave plate to rotate thepolarization of the first beam to be the same as the second linearpolarization; and a plurality of prisms positioned proximate to thepolarization beam splitter to redirect the second beam to travel in thefirst direction along with the first beam.
 15. The system of claim 10,wherein the optical assembly comprises: a collimating lens to collimatethe unpolarized optical radiation; a polarizing beam splitter to splitthe collimated optical radiation into a first beam with a first linearpolarization traveling in a first direction and a second beam with asecond linear polarization orthogonal to the first linear polarizationalso traveling in the first direction; and a half-wave plate to rotatethe polarization of the first beam to be the same as the second linearpolarization.
 16. The system of claim 15, wherein the optical assemblyfurther comprises: an optical element to deflect the first and secondbeams onto the tunable optical metasurface.
 17. The system of claim 16,wherein the optical element comprises one of a mirror and a prism. 18.The system of claim 10, wherein the refractive index tunable dielectricmaterial comprises liquid crystal.
 19. The system of claim 18, wherein acontroller is configured to tune the tunable optical metasurface byselectively applying different voltages to the elongated rails togenerate a voltage differential bias pattern within the liquid crystalbetween the elongated rails.